Manufacturing of Carbon Nanotube Preform with High Porosity and Its Application in Metal Matrix Composites
2017 Volume 58 Issue 5 Pages 834-837
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2017 Volume 58 Issue 5 Pages 834-837
A new process is proposed to manufacture carbon nanotube preform and carbon nanotube (vapor grown carbon fiber, VGCF)-reinforced aluminum matrix composite. Carbon nanotube preform is fabricated using a mixtures of mesophase pitch (MP) and VGCF. The VGCF-MP-preform-reinforced aluminum composite was manufactured by a low-pressure casting method, with a pressure of 0.8 MPa. The effect of the addition ratio of MP powder and VGCF on VGCF-MP-preform was observed. Therefore, microstructure of VGCF-MP-preform-reinforced aluminum composites with and without nickel plating was observed.
Recently, there has been a rapid advanced in high-output electronic and control devices, with an increase in power consumption. Metal matrix composites (MMCs) have been utilized in many fields, such as: a heat sink for the powering devices of hybrid vehicles, electric vehicles and diode; a tray component for manufacturing and inspection equipment of the semiconductor, liquid crystal panel and solar battery. These field materials exhibit a better performance than metal. Carbon fiber-reinforced copper composite (C/Cu)1), carbon fiber-reinforced aluminum-based composite (C/Al)2), carbon fiber-reinforced epoxy resin composite (C/Ep)3) and silicon carbide-reinforced aluminum matrix composite (SiC/Al)4) were developed as heat dissipation material. However, solder fracture occurred due to the mismatch in thermal expansion coefficient (CTE) between the semiconductor and the C/Cu composite. C/Al, C/Ep and SiC/Al composite have low workability. Therefore, development of new manufacture method is needed using a carbon nano tube, which has low CTE and good workability. The objective of this study was to develop a new manufacturing process for VGCF-MP-preform and VGCF-MP-preform-reinforced aluminum matrix composite. The microstructure of VGCF-MP-preform-reinforced aluminum composites was observed.
Pure aluminum (A1070), with high thermal conductivity, high workability and light weight, was used as the matrix. NaCl (particle size : 180～355, 600～700 μm) was used as a spacer material in this experiment. Figure 1 shows SEM images of VGCF, MP powders and NaCl (180～355, 600～700 μm). VGCF, with a diameter of 150 nm and a length of 10～20 μm, has a high thermal conductivity, low CTE and low cost as the reinforcement (VGCF, Showa Denko KK), MP powder (JFE Chemical Corporation), with 2 μm particle diameter, was used for connecting the VGCF. The lattice spacing of the as-received MP and VGCF (002) planes are investigated using X-ray diffraction (XRD; JEOL JDX-11RA, CuK¡, 40.0 kV, 40 mA). The MP powder was subsequently heated at 793 K for 1 h in vacuum, at less 40 Pa, to determine the effect of heating on MP crystallization. The (002)-plane lattice spacing of the heated MP was then investigated using XRD. VGCF-MP-preform microstructures were observed using scanning electron microscopy (SEM; Hitachi, S-5200, 615 kV). The structures of the VGCF surface and the interface between the VGCF and MP were observed using a transmission electron microscopy (TEM; JEOL JEM-2010, 200 kV). Nanostructures on the VGCF surface were analyzed using an inverse fast fourier transform (IFFT) by Digital Micrograph software.
SEM images of VGCF, MP Powders and NaCl (180～355, 600～700 μm).
VGCF-MP-preform was produced using the following four steps. First, VGCF and MP were mixed by a stirrer machine in ethanol, for 600 s, before being subjected to ultrasonic cleaning for 1800 s with an acetone solution. Second, NaCl powder was added to the mixture as a spacer material and stirred for 600 s. Third, the mixed powder (VGCF, MP, NaCl) was put in a graphite mold and pressed at 75 MPa and then it was heat-treated at a temperature of 793 K, for 1 h. Fourth, the sintered compact was immersed in distilled water to remove NaCl powder. Table 1 shows the fabrication conditions of VGCF-MP-preform.
| Amounts ratio of NaCl (Vol%) |
MP:VGCF (Vol%) |
Size of pore (μm) |
Nickel plating |
|---|---|---|---|
| 70 | 10 : 0 | 180～355 | - |
| 7 : 3 | 600～700 | Treated | |
| 180～355 | Non-treated | ||
| Treated | |||
| 5 : 5 | 180～355 | - | |
| 3 : 7 | 180～355 | - |
Nickel electroless plating was carried out on the VGCF-MP-preform surface for improvement the wettability with the molten Al. Before nickel-electroless-plating, the VGCF-MP-preform was immersed in acetone solution for 300 s, subsequently being ultrasonic cleaned for 300 s with distilled water and dried for 120 s. It was then immersed in 10% HNO3 solution, Sn solution and Pd solution for 300 s, ultrasonic cleaned for 300 s with distilled water and dried for 120 s before being pretreated. Nickel electroless plating of VGCF-MP preform was carried out at a temperature 293 K for 300 s and at 353 K for 300 s, at a PH of 6.5. Finally, the VGCF-MP-preform-reinforced aluminum composite was manufactured at a pressure of 0.8 MPa and molten aluminum at a temperature of 973 K, in Argon gas.
Figure 2 shows the SEM images of VGCF-MP-preform frame, with the addition ratio of MP : VGCF being 10 : 0, 7 : 3, 5 : 5 and 3 : 7 (vol%). With regard to the MP powder (Fig. 2 (a)), it was sintered at 793 K, as its softening temperature is 623 K, which can be used for binding of VGCF and VGCF. However, micro-pore by vaporization of impurity inside MP powder by heat-treatment was observed inside the frame of preform. With the addition ratio of MP:VGCF = 7 : 3 vol%, a cross-linked structure of VGCF and MP was observed in Fig. 2 (b). However, with the addition ratio of MP : VGCF = 5 : 5 and 3 : 7 vol%, cracks and deformations were observed on surface of the VGCF-MP-preform, as shown in Fig. 2(c) and (d), because the uncross-linked VGCF occurred by decreasing the addition amount of MP powder. All of the shape of the pores inside preform are the same of NaCl powder like Fig. 1 (c). Figure 3 shows the SEM images of VGCF-MP-preform, with MP : VGCF = 7:3 vol%. Defects and cracks were not observed in the preform. From Fig. 3(a), the pores of the square shape and 180～355 μm size were observed. It is the same size and shape as the NaCl powder used spacer material. The enlarged portion of a frame of VGCF-MP-preform is shown in Fig. 3(b), where the cross-linked structure of VGCF and MP can be observed. This cross-linked structure was expected to improve of flowing of heat. In Fig. 3(c), MP enclosed, rather than bridging, the VGCF, which were randomly oriented in the MP. Figure 4 shows the results of low-magnification, high-magnification TEM images of preform and IFFT patterns for carbon surface structures in preform. Figure 4(a) shows that the VGCF were crosslinked by the bridging MP. The VGCF surfaces were covered with a thin MP layer, which formed the bridging. Figure 4(b) shows the VGCF-MP interface, consisting of linear and wavy carbon structures, in the VGCF-MP-preform. IFFT analyses were used to determine the interfacial structures between the VGCF and MP. Figure 4(c) shows the results of these analyses. The wavy structure showed dislocation near the VGCF-MP interface. MP is believed to bridge the VGCF by combining the free carbon atoms in the MP with the dangling bonds, which are empty valence orbitals on the surface of immobilized atoms at the VGCF dislocation edges.
SEM images of preform after spacer method, MP:VGCF is 10 : 0, 7 : 3, 5 : 5 and 3 : 7 (vol%).
SEM images of preform after spacer method, MP : VGCF is 7 : 3 (vol%).
Low-magnification (a), high-magnification TEM images of preform (b) and IFFT patterns for carbon surface structures in preform (c) (d).
Figure 5 shows XRD patterns for the as-mixed and heated VGCF-MP mixtures. The shape of the peak attributed to the (002) plane in the XRD pattern for the as-mixed VGCF-MP mixture, was similar to that of the one attributed to the (002) plane of pure VGCF, with the peak overlapping the one attributed to MP. The peak attributed to the (002) plane in the XRD pattern for the heat-treated VGCF-MP mixture, on the other hand, was narrower than those attributed to the heated monolithic MP and the as-mixed VGCF-MP mixture, while being similar to the XRD peak attributed to a single material, indicating that the heated VGCF-MP mixture showed significantly improved crystallinity.
XRD patterns for as-received MP, heated MP, VGCFs, as-mixed and heated VGCF-MP.
Figure 6 shows the results obtained by performing the nickel electroless plating of the VGCF-MP preform of MP : VGCF = 7:3 vol%. With regard to point analysis by EPMA, it was observed that the pores and frame of the VGCF-MP-preform made with MP and VGCF were nickel electroless plated. The thickness of nickel electroless plating was at least 30 μm, in the internal direction of the VGCF-MP-preform. This means that the plating solution infiltrated by the capillary phenomenon of micro pores, which was caused by the intertwining of MP and VGCF.
SEM images and EDS analysis of nickel plated preform.
Figure 7 shows the SEM images of VGCF-MP-preform-reinforced aluminum composite with no-nickel-plating (pore size, 180～355 μm), (b) with nickel-plating (pore size, 180～355 μm). And (d) with nickel-plating (pore size, 600～700 μm). From the interface of aluminum and VGCF-MP-preform in no-nickel-plating composite, defects were observed. However, VGCF-MP-preform-reinforced aluminum composite with nickel-plating, defects were not observed. Molten aluminum was made to infiltrate into pores, which has manufacturing by NaCl powder. The diffusion of nickel was detected inside the frame of VGCF-MP-preform. This is how the wettability of aluminum with VGCF was improved nickel plating without defects.
SEM images of VGCF-MP-preform-reinforced aluminum composites; pore size, 180～355 μm without nickel plating (a), pore size, 180～355 μm with nickel plating (b) and pore size, 600～700 μm with nickel plating (c).
To overcome the disadvantages of the conventional method of manufacturing carbon nanotube-reinforced metal matrix composite, a new method for fabricating an aluminum matrix composite reinforced with vapor grown carbon fiber preform by low-pressure casting was developed. The significant results are below.
(002)-plane lattice spacing of the MP was remarkably decreased when heated to 793 K. The VGCF-MP-preform showed narrow (002)-plane lattice spacing, compared to that of the VGCF. MP enclosed, rather than bridging, the VGCF, which were randomly oriented in the MP. VGCF microstructures consisted of linear and wavy carbon structures. The results of IFFT analysis suggest that the wavy structure showed dislocation.
The VGCF-MP-preform was produced by the addition amount of the VGCF, MP and NaCl, in the proportion was NaCl : Powder = 7 : 3, MP : VGCF = 7 : 3 (vol%). The thickness of nickel plating was 30 μm in the internal direction of VGCF-MP-preform. The wettability between the aluminum and VGCF was improved by nickel plating, while no defects were observed in the interface of aluminum and VGCF-MP-preform. Thus, a new manufacturing process for VGCF-MP-preform-reinforced aluminum composite with low pressure casting was developed.
